Questions

‘Unless’ is used to denote the condition i.e. ‘If’...... ‘Not’. So, again the use of negative word ‘not’ is superfluous. So, the phrase, ‘are not very’ needs to be replaced with ‘are very’ to make the sentence grammatically correct. Thus, the correct formation would be, ‘Unless, you are very careful, you will run into debt’.

If some action has started in the past and is still continuing, then present perfect continuous tense should be used instead of present continuous tense. So, the phrase ‘am waiting’ needs to be replaced with ‘have been waiting’ to make the sentence contextually correct. Thus, the correct formation would be, ‘I have been waiting for three –quarters of an hour’.